As produced at the wellhead, crude oils contain substantial quantities of inorganic particulate solids and water, and it has long been standard practice to require that the combined solids and water (BS&W) content be reduced to a value not exceeding a stated small percentage before the crude is introduced into a pipeline or supplied to a refinery. Such reduction of the BS&W content is necessary both to minimize damage to pipeline and refining equipment from, e.g., corrosion and abrasive wear, and to minimize economic losses arising from transporting and processing the non-petroleum constituents making up the BS&W content. Though specifications vary among localities and refineries, a typical specification requires that the BS&W content of the crude not exceed 0.5% by volume.
The BS&W content of many crudes can be brought within specifications relatively simply and easily, as by gravitational separation and, when required, addition of various treating agents. However, the heavy oil crudes, and especially those produced by fireflooding or other thermal recovery practices, have presented a more serious problem and no completely satisfactory method has been available for reducing the BS&W content of such crudes. Such crudes are highly viscous, so that the raw crude must in all events be diluted with, e.g., a wide gasoline fraction, commonly called condensate, to achieve adequate fluidity for handling and treatment. Even thus diluted, however, simple settling operations, even for extended times, do not result in adequate separation of the water from the oil, and it is commonly recognized that a substantial part of the remaining water is present as the disperse phase of a stable water-in-oil emulsion. In many cases, attempts to break the emulsions in such crudes have met with little success, and much attention has been given to the emulsion breaking problem by workers in the field. Prior to the invention disclosed in this application and the related applications listed above, attempts to bring the crudes within pipeline specifications have centered mainly on the dilution of the crude, preliminary separation of a major portion of the free water from the diluted crude, and use of one or more treating agents, commonly called demulsifiers in the trade, intended to break the water-in-oil emulsion of the crude so that separation of the emulsified water and the particulate solids could be accomplished. Particularly in the case of the heavy oil crudes, and especially those produced by fireflooding or other thermal procedures, prior art efforts have met with little success. Thus, taking fireflood crudes from the Husky Aberfeldy field as an example, testing of all of the demulsifiers offered by oilfield service companies has failed to provide a successful treatment.
As disclosed in aforementioned copending application Ser. No. 522,651, it has been found that the water-in-oil emulsions of the difficulty treatable heavy oil crudes, such as the Aberfeldy fireflood crudes, appear not to be stabilized by clays or other particles heretofore blamed for the stability of the emulsions, since the water globules of the disperse phase of the emulsions tend to be small in comparison to the particle size of the clays, silica and like native particulates of the crude. As a result of that discovery, a method was developed for breaking such emulsions, using an agent such as ammonium bisulfite when the pH of the crude had been raised to at least 8, advantageously to at least 10, as by the addition of an aqueous solution of sodium hydroxide. That method has for the first time been successful in reducing to pipeline specifications the BS&W content of a wide range of heavy oil crudes, especially those produced from the Cretaceous reservoirs in the Western Canada sedimentary basin, including the Cold Lake, Lloydminster and Medicine River fields. Further, as described in aforementioned U.S. Pat. No. 4,466,885, it has been discovered that, once the emulsion of the crude has been destabilized, as by use of ammonium bisulfide at an elevated pH, reduction of the BS&W content can then be adied by use of one of the conventional demulsifiers, namely, that supplied by Champion Chemical Co., Edmonton, Alberta, Canada, as CHAMPION BX6079, though most conventional demulsifiers appear to be of no assistance. The demulsifier supplied as CHAMPION BX6079 is a proprietary composition believed to be based upon mixtures of aliphatic and aromatic glycols in xylene as a diluent, the compounds being polar, soluble in oil and exhibiting surfactant action at the interfaces between the disperse water globules and the continuous oil phase of the emulsion in the crude. Demulsifiers supplied under the trademarks TRETOLITE RP663 and TRETOLITE RP514 have also been found to offer assistance.
Since the conventional demulsifiers are relatively expensive and, with few exceptions, of little value in the treatment of heavy oil crudes, there is a continuing need for discovery of new, effective demulsifiers and methods to aid in treatment of crudes by, e.g., the methods disclosed in the aforementioned copending applications.